The present application relates to an optical element covering member, a backlight, and a liquid crystal display device, the latter two of which include the above optical element covering member, and more particularly relates to an optical element covering member which improves display properties of a liquid crystal display device.
Heretofore, in a liquid crystal display device, many optical elements are used in order to improve the viewing angle, the luminance, and the like. As the optical elements, for example, films and/or sheets, such as a diffusion film and/or a prism sheet, have been used.
FIG. 23 shows the structure of a related liquid crystal display device. This liquid crystal display device has, as shown in FIG. 23, a lighting element 101 emitting light, a diffusion plate 102 diffusing the light emitted from the lighting element 101, a plurality of optical elements 103 condensing and/or diffusing the light which is diffused by the diffusion plate 102, and a liquid crystal panel 104.
In recent years, concomitant with an increase in size of an image display device, the weight and the size of an optical element tend to be increased. When the weight and the size of an optical element are increased as described above, the rigidity thereof becomes insufficient, and as a result, the optical element is unfavorably deformed. The deformation of the optical element as described above has adverse influence on light directivity to a display surface, and a serious problem, so-called luminance irregularity, may arise.
Accordingly, it has been proposed that by increasing the thickness of an optical element, insufficient rigidity is improved. However, since the thickness of a liquid crystal display device is unfavorably increased, advantages thereof, such as a small thickness and light weight, are diminished. Hence, it has also been proposed that by bonding optical elements to each other by a transparent adhesive, insufficient rigidity of each optical element in the form of a sheet or film is improved (for example, see Japanese Unexamined Patent Application Publication No. 2005-301147).
However, according to the technique disclosed in Japanese Unexamined Patent Application Publication No. 2005-301147, since the optical elements are bonded to each other by a transparent adhesive, the thickness of the liquid crystal display device itself is also increased although the increase is not so much as that by the above method in which the thickness of the optical element itself is increased. In addition, by the use of the transparent adhesive, display properties of the liquid crystal display device may be degraded in some cases. Furthermore, since the number of manufacturing steps is increased, the yield of non-defective products may be seriously influenced, for example, by dust contamination which may occurs during a bonding step.